The present invention relates generally to a system and method for inspecting cigarettes, and more particularly, to a system and method for detecting the length of various sections within cigarettes.
To ensure a high quality product, some cigarette manufacturers optically inspect the cigarettes at various stages of production using a video camera. The images obtained from the video camera may then be fed to a digital computer and analyzed for the presence of various imperfections (i.e., departures from expected specifications). U.S. Pat. Nos. 5,235,649, 5,366,096, 5,414,270, 5,013,905 and 4,976,544 exemplify this technique. For instance, U.S. Pat. No. 5,235,649 forms a digital image of the end of a tobacco plug of a cigarette. This technique then determines the standard deviation of the pixel values within the image. The standard deviation is used to quantify how firmly the tobacco is packed within the cigarette. Other techniques image the surface of the cigarette paper and detect pinholes or blemishes on the cigarette paper through image analysis.
The above described techniques provide useful information regarding the external surface of the cigarette, but fail to detect internal imperfections. For instance, with reference to FIG. 1a, the cigarette 2 discussed in commonly assigned U.S. Pat. No. 5,388,594 comprises a tobacco plug 4, a hollow void chamber 6, a hollow acetate tube 8 and a mouthpiece filter element 10, all surrounded by various layers of cigarette paper 9. The paper 9 conceals the underlying cigarette sections. As such, defects in the length of these various sections can not readily be ascertained by an inspection of the exterior of the cigarette.
To overcome this drawback, some manufacturers take random samples of cigarettes at various stages of their production and dissect the cigarettes. A technician then measures the dimensions and spacings of the internal sections. However, cutting into the cigarettes often disturbs the spacing of the sections, and thereby obscures the boundary between different sections. Moreover, often different technicians employ different measuring techniques, sometimes producing conflicting measurements for the same cigarette.
Some practitioners in the art have proposed the use of optical systems for detecting the internal properties of cigarettes. Typically, these techniques entail directing a beam of electromagnetic radiation through the cigarette at one or more localized points on the cigarette. A photodetector receives the electromagnetic radiation which passes through the cigarette. The output of the photodetector, in turn, may be processed to reveal a characteristic of the cigarette. For instance, U.S. Pat. No. 5,010,904 proposes transmitting infrared radiation through the tip of a cigarette tobacco plug. A separate detector element receives the infrared radiation after it passes through the tip. The output of the detector is then fed to a comparator which compares the output of the detector with a threshold value. A measured value below the threshold value reflects a loosely packed tobacco plug. U.S. Pat. Nos. 4,001,579, 4,986,285, and 4,212,541 propose similar techniques.
Because of the relative simplicity of the above described techniques, they fail to provide reliable information regarding the boundaries between adjacent cigarette sections, especially where those boundaries are somewhat ambiguous. More specifically, by narrowing the focus of the investigation to a limited point on the cigarette, these techniques fail to provide an indication of various imperfections which can only be detected by examining the cigarette as a whole (e.g., by taking into account the spatial relationships between different sections of the entire cigarette).
Accordingly, it is an exemplary objective of the present invention to provide a system and method for accurately inspecting the internal sections of a cigarette which accurately reflects the dimensions of the internal sections of cigarettes. It is a more specific exemplary objective of the present invention to provide a system and method for efficiently and reliably providing the measurements M1, M2, M3, M4, and M5 shown in FIG. 1b, corresponding, respectively, to the length of the filter element 10, the length of the hollow acetate tube 8, the length of the void 6, the length of the tobacco plug 4, and the overall length of the cigarette 2. It is a further objective of the present invention to alert the user when any of these measurements differ from their expected values by more than a prescribed amount.